好像是初中的数学吧。这么小就会用百度干这个了！不错令x/2=y/3=z/4 =kx=2k,y=3k,z=4k带入（x+y+z）/（x-2y+2z）中(2k+3k+4k)/(2k-6k+8k)=9k/4k=2.25
x/2=y/3=z/4z=2x,y=1.5xx+y+z/x-2y+2z=x+1.5x+2x/(x-3x+4x)=4.5x/2x=2.25
